We’ve recently added support for flagging high “JavaScript boot-up time” to Lighthouse. This audit highlights scripts which might be spending a long time parsing/compiling, which delays interactivity. You can look at this audit as opportunities to either split up those scripts, or just be doing less work there.

Another thing you can do is make sure you’re not shipping unused code down to your users:

Code coverage is a feature in DevTools that allows you to discover unused JavaScript (and CSS) in your pages. Load up a page in DevTools and the coverage tab will display how much code was executed vs. how much was loaded. You can improve the performance of your pages by only shipping the code a user needs.